Organisation of an ecosystem — AQA GCSE Combined Science: Trilogy

Revision notes

4 short notes, in the order of the specification. Each one in short:

1. Producers, consumers and food chains

   A food chain represents the feeding relationships within a community. All food chains begin with a producer, usually a green plant or alga, which makes glucose by photosynthesis. Primary consumers eat the producer, secondary consumers eat the primary consumers, and tertiary consumers eat the secondary consumers. Consumers that kill and eat other animals are predators, and those eaten are prey.

2. Sampling: distribution and abundance

   Practical

   Quadrats and transects are sampling methods used to find the distribution and abundance of species. A quadrat is a square frame placed at random positions to count organisms and estimate population size. A transect is a line with quadrats placed at regular intervals along it, showing how a species changes as a factor such as light intensity changes.

3. Predator-prey cycles

   Predator-prey cycles are the regular rise and fall in the numbers of predators and prey in a stable community. When prey numbers are high, the predators have plenty of food, so their numbers rise. More prey are then eaten, so prey numbers fall, and with less food the predator numbers fall too. On a graph, the prey peak comes first.

4. How materials are cycled

   The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide, to be used by plants in photosynthesis. Carbon passes along food chains, and plants, animals and decomposing microorganisms release carbon dioxide by respiration. The water cycle provides fresh water for plants and animals on land through evaporation and precipitation. Decomposers also return mineral ions to the soil.